The invention is directed to a soot blower for cleaning the interior surfaces of a boiler by discharging a suitable cleaning fluid from a nozzle against such surfaces. More particularly, the invention relates to new and improved mechanisms for driving and guiding the lance tube mounting the fluid discharge nozzle of the soot blower from a non-working position forwardly through a working motion and return.
Typically, in a soot blower of the long retracting type, a lance tube is moved through a long, e.g., 65 foot path of travel horizontally forward into the heat exchange zone of a large public utility boiler. During the traveling motion of the lance tube, the tube is rotated about its longitudinal axis and a cleaning fluid is discharged through a nozzle mounted at the forwardmost end of the tube so that the fluid may be directed against various internal surfaces of the boiler to remove undesirable soot accumulations. Accordingly, various means are required for imparting movement to the lance tube and for guiding the long lance tube as it enters and leaves the boiler.
It is one objective of the present invention to provide a novel cable drive system for the lance tube. Generally, the system comprises a two-cable arrangement having first and second drive cables. The first cable includes one end fastened to the traveling carriage which supports the lance tube for horizontal movement. The first cable extends from the traveling carriage around the pulley of a cable tensioner, mounted proximate to the rearmost non-working position occupied by the traveling carriage, to a fastened relation with a rotatable drum of a traversing drive assembly. The second cable also includes an end fastened to the traveling carriage and extends from the traveling carriage around the pulley of a second cable tensioner, mounted near the forwardmost position occupied by the traveling carriage, to a fastened relation with another part of the rotatable drum. In accordance with a feature of the invention, the rotatable drum is provided with a grooved cylindrical cable-receiving surface so that several complete cable wraps of each of the first and second cables may be wound around the rotatable drum.
A suitable electric drive motor is mechanically connected to the rotatable drum through appropriate gearing mechanisms whereby the drum may be driven through a clockwise or counter-clockwise rotation. When the rotatable drum is rotated through a clockwise rotation, the second cable is taken up by the rotating drum causing the cable to pull the traveling carriage forwardly, thereby advancing the lance tube into the boiler. When the lance tube has been fully inserted into the boiler, the rotatable drum may then be rotated in the counter-clockwise direction causing the first cable to be wound onto the drum whereby the first cable will pull the traveling carriage rearwardly back towards the non-working position, thereby retracting the lance tube from the boiler. Pursuant to the invention, the rotatable cable drum is positioned midway between the rearwardmost and forwardmost points on the path of travel for the traveling carriage. Accordingly, the length of each of the first and second cables may be kept at a minimum. The central location of the rotatable drum and relatively short length for each of the cables minimizes unwanted vibrations and harmonics which may develop during operation of the cable drive system. Moreover, the grooved surface for the cable drum prevents any section of either of the cables from coming into direct contact with any other section of the cables to eliminate cable scrubbing. This reduces wear and tear on the cables and lengthens the useful worklife of the cables. To advantage, the cable tensioners are adjustable to accommodate cable stretch thereby avoiding sagging of the cables to assure long term successful operation of the cable drive.
As another feature of the invention, a movable guide system is provided to guide the cables onto and off the rotatable drum. The guide assembly includes traveling assemblies that follow a complementary cable across the surface of the drum to insure that the cable is properly received in the grooved portions of the drum surface. The assemblies also tend to dampen any vibrations in the cables to facilitate their motion onto and off the drum. This acts to further reduce wear and tear on the cables and permits the cables to be positioned close to the top of the soot blower housing with sufficient clearance for the cable to pass into and out of the housing.
In accordance with another significant feature of the invention, a revolving roller assembly is provided to guide the lance tube into and out of the boiler. The revolving roller assembly is mounted adjacent the boiler at the lance-tube-receiving opening thereof and comprises three rotatable rollers, each including a generally concave surface. The rollers are rotatably mounted in a circular frame with each roller being in a spaced, opposed relation to the other rollers. The rollers are arranged and configured whereby the axis of each of the rollers forms an angle of approximately 60.degree. with the axis of each of the adjacent two rollers. In this manner, the concave surfaces of the opposed rollers define a generally circular central opening whereby the lance tube may be received through the opening to be supported and guided by the rotatable rollers into the boiler. The circular frame mounting the rollers is in turn rotatably mounted in a supporting structure so that, as the rotating lance tube is guided into the boiler by the rollers, the entire circular roller supporting frame may be rotated with the lance tube to substantially reduce friction between the lance tube and guiding rollers.
During the horizontal movement of the long lance tube, the tube is guided through a curved path of travel outside the boiler so that the torque developed by the free nozzle end of the tube, as it moves forwardly and upwardly into the boiler, will counteract the upward motion the curved path tends to impart to the nozzle. The net effect is to maintain the nozzle in a generally more linear path within the boiler and to prevent the nozzle from drooping excessively as it advances toward its furthest position within the boiler.
In a typical soot blower of the long retracting type, a feed pipe is arranged in a co-axial, telescoping relation with the lance tube to provide fluid communication between the lance tube and a source of cleaning fluid. The above-described curved path of travel for the lance tube tends to bend the feed pipe into a curved pipe, thereby creating large, concentrated radial loads between the forwardmost end of the feed pipe and the lance tube. These concentrated loads cause high friction and excessive bearing wear and eventually lead to scratching of the feed pipe, packing failure and fluid leakage. Pursuant to another feature of the invention, the adverse radial load is greatly eliminated by a self-aligning feed pipe housing interposed between the forwardmost end of the feed pipe and the lance tube. The bushing includes novel spherical radii cut into the outer diameter of the bushing whereby the bushing may follow the bend of the curved feed pipe and distribute the load over a greater area.
Another advantageous feature of the invention includes an improved valve assembly arranged between the feed pipe and the source of cleaning fluid. Generally, the valve assembly comprises an unbalanced main valve plug with the high pressure of the fluid on the input side of the valve plug tending to hold the plug in a closed position. The plug includes a smaller, inner auxiliary plug which is opened initially to equalize pressure on both sides of the plug so that when the main plug is lifted from the valve seat, there are no great unbalanced fluid pressure forces resisting the opening movement. Thus, the unbalanced valve assembly will insure a tight, closed condition for the valve while the inner plug arrangement facilitates an easy valve opening and closing operation.
The present invention provides several features, each with numerous advantages to enhance the effectiveness and reliability of a soot blower in achieving its intended purpose. The many features of the invention compliment one another in an overall system for driving and guiding the lance tube resulting in smooth and efficient operation. The cable drive offers a straightforward traverse motion for the lance tube while the revolving roller assembly facilitates low friction entry of the lance tube into the boiler. These features, when coupled with the wear-reducing effects of the novel self-aligning feed pipe bushing and the efficacious operation of the unbalanced valve plug insure long term, dependable boiler cleaning by the soot blower.
For a better understanding of the above and other features and advantages of the invention, reference should be made to the following detailed description of a preferred embodiment of the invention and to the accompanying drawings.